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Water Quality

Welcome to the NPDES Water Quality information page. Described below are the various water quality requirements that must be met throughout the project development and construction process. You will be provided a single point of contact during each of these phases. Should you have any questions, please contact our Customer Service line (714) 667-8888.

Discretionary Application Process

  • Review of projects for water quality requirements
  • Application of Conditions of Approval

Plan Check

  • Water Quality Management Plan (WQMP)
  • Erosion and Sediment Control Plan (ESCP)

Construction Site Inspections

  • Implementation of construction phase BMPs
  • NPDES Inspections

Post-Construction Operation and Maintenance of BMPs

  • 12-month post-construction inspection

The County’s NPDES Program enforces State mandated water quality regulations that apply to construction projects in the unincorporated area. These regulations are intended to minimize pollutants and runoff from both construction sites and completed project sites. The County has established requirements that owners, developers, contractors and builders must meet at each stage of the project development process in order to achieve compliance. These NPDES requirements have been integrated into the project application/permit approval process and construction site inspection system. These requirements include the following:

  • Non-exempt projects must prepare and submit a project specific Water Quality Management Plan (WQMP) prior to the issuance of any grading or building permit. The WQMP describes the permanent, post-construction Best Management Practices (BMPs) that will be constructed or utilized on the site and maintained during the life of the project.
  • An Erosion and Sediment Control Plan (ESCP) must be submitted with each set of grading and building plans submitted for Plan Check. The ESCP describes the appropriate BMPs that will be used throughout the construction (grading and building) phase.
  • NPDES inspections will be conducted on all construction sites to ensure that appropriate BMPs are kept in place throughout the construction phase. The frequency of these inspections is regulated by a State mandated schedule for both wet and dry seasons.
  • After construction has been completed, property owners are responsible for the ongoing operation and maintenance of all structural and non-structural water quality BMPs on their property and may be required to obtain a 12-month post-construction inspection of treatment control BMPs.

Not sure which region your property/project is in? Click here to use this link and your address to find out!


South Orange County Revised Water Quality Requirements (effective September 28, 2017) 


Each project proponent must implement a program that requires and confirms structural BMPs on all Priority Development Projects are designed, constructed, and maintained to remove pollutants in storm water to meet the criteria set forth in Model WQMP, TGD, and HMP, accessible at the links below.

Below, please find links to download the September 28, 2017 versions of the land development documents:

Model WQMP, TGD, and HMP 

For the latest Model WQMP, TGD, and HMP, please visit the OC Watersheds website.

Templates and Checklists        

MSWord Versions of TGD Worksheets


Non-Priority Projects are projects that do not meet any of the categories to be called a Priority Project (Technical Guidance Document Section 1.2), and (3) have a non-negligible potential for stormwater pollution.

The Orange County Stormwater Program has developed this Non-Priority Project Water Quality Checklist for new development / significant redevelopment projects in the San Diego Permit Region classified as Non-Priority Projects. These projects are required under the San Diego Regional Board MS4 Permit (South Orange County Permit) to incorporate applicable site design and source control BMPs. This template serves as a mechanism to document the incorporation of site design, source control and any other BMPs.

This checklist is provided to help the project applicant summarize basic project information, identify applicable source control and site design BMPs, and determining maintenance requirements for these BMPs.

Non-Priority Project proponents are required to complete this checklist or other documentation for local jurisdiction review and approval. Applicable sections of the Technical Guidance Document (TGD) are referenced for assistance with completing each section of the checklist.


South Orange County Hydromodification Requirements (September 28, 2017)

Hydromodification Criteria for Priority Development Projects in the San Diego Regional Water Quality Control Board Jurisdiction

In addition to preparing a Project WQMP for Priority Development Projects, all Priority Development Projects* in the San Diego Region are required to comply with hydromodification criteria. The goal of hydromodification control is to integrate hydrologic controls into a proposed project such that the flow duration curve corresponding to the post project condition agrees with the baseline condition curve over the range of flows of interest. This range is 10% of the 2-year peak flow (0.1Q2) to the 10-year peak flow (Q10). The baseline condition is the pre-development condition, which is typically oak grassland habitat.

Hydromodification control criteria are described in the TGD and HMP, linked above.

A hydrologic model called the south Orange County Hydrology Model (SOCHM) has been developed to assist project proponents in selecting and sizing hydromodification controls.

South Orange County Water Quality Requirements (prior to September 28, 2017)


North Orange County Revised Water Quality Requirements (effective August 17, 2011)

Water Quality (NPDES) Information